Biorefineries producing commodities from renewable resources offer an alternative to oil refineries based on dwindling supplies of petroleum and permit a move towards improved energy security. Lignocellulosic materials from forestry and agriculture are attractive as feedstocks, since they are abundant, relatively inexpensive, and are not used for food. Lignocellulose consists mainly of lignin and two classes of polysaccharides, cellulose and hemicellulose. The polysaccharides can be hydrolyzed to sugars and converted to various fermentation products, such as bioalcohols, in processes based on biocatalysts, such as the industrially important baker's yeast (Saccharomyces cerevisiae).
The hydrolysis of cellulose is typically preceded by a pretreatment, in which the hemicellulose is degraded and the cellulose is made increasingly accessible to cellulolytic enzymes or acidic hydrolysis. Enzymatic hydrolysis of lignocellulosic materials is considered the most promising method to obtain a high yield of glucose from cellulose. By using enzymatic hydrolysis, hydrolysis and fermentation can be performed simultaneously in a simultaneous saccharification and fermentation (SSF) process or in a consolidated bioprocess (CBP). Alternatively, separate hydrolysis and fermentation (SHF) can be used, a process configuration that may also include enzyme-based hydrolysis of the cellulose.
To obtain high yields of sugars from lignocellulosic substrates, dilute acid hydrolysis pretreatment and/or steam pretreatment with acid catalysts are considered appropriate pretreatment methods. Furthermore, in industrial processes for converting lignocellulosic biomass to fermentation products, such as cellulosic ethanol, the whole slurry obtained after pretreatment will probably be used at a high solids concentration. However, the pretreatment liquid is known to inhibit enzymatic hydrolysis.
Previously, addition of surfactants has been considered for improving enzymatic saccharification of cellulosic substrates. Surfactants probably prevent unproductive binding of enzymes to complex lignocellulosic substrates, such as pretreated wood. The economical benefit of adding surfactants to reaction mixtures intended for production of yield-sensitive low-value-added products such as liquid biofuels has, however, been questioned.
The addition of enzymes constitutes a considerable part of the total cost for the process of producing products from lignocellulosic material. The cost for enzymes is for instance regarded as one of the main obstacles for industrial implementation for conversion of lignocellulose to liquid biofuels. It would therefore be desirable to improve the efficiency of the enzymatic hydrolysis of lignocellulosic materials, e.g. to obtain more sugars from a certain enzyme dosage and time period, or to obtain the same amount of sugars from a lower enzyme dosage for the same time period. It is also desirable to achieve a certain amount of sugars with a certain enzyme dosage in a shorter time period, since this increases the production capacity and thereby allows for improved production and/or decreased costs of investment. Improving the efficiency of the enzymatic hydrolysis of cellulose may significantly contribute to commercialization of products based on lignocellulose-derived sugars.